Workers who deal with pathogenic or dangerous materials must often be completely isolated from their external environment. The same restriction applies to many other situations, as with recently sterilized medical equipment. The usual method of ensuring isolation is via an impermeable plastic membrane. These membranes, however, are vulnerable to punctures or tears that compromise their utility. In many cases, these punctures occur without the knowledge of the user, who continues to use the enclosure, assuming that it is intact.
Previous attempts to provide a visual indication of the rupture of a plastic membrane include U.S. Pat. No. 4,986,429 issued to Singleton (1991), which discloses a material for wrapping the necks of pharmaceutical bottles which consists of a series of longitudinally arranged, pressurized sacs of dye arranged around the neck of the bottle, which dispense their dye upon being ruptured. There are a number of disadvantages to this design, however. The membrane is expensive and difficult to make. Once made, it has a great weight. It also has limited mobility-creasing or folding the material is likely to rupture one or more of the sacs. The sacs are sensitive to temperature and pressure. Moreover, it is also a destructive notification. Once the material has been ruptured in one location, the entire apparatus must be discarded. Forming complex shapes (such as a suit or glove) would also be difficult and expensive using this material.
U.S. Pat. No. 4,930,522 issued to Busnel, et al. (1990) describes a prophylactic device consisting of inner and outer barrier membranes separated by a layer of a pharmacologically active substance. The assumption is that any rupture of the membrane will release the substance, thereby mitigating the effects of the rupture. Presumably, dye could replace the substance, providing a visible indication of a tear. There are a number of disadvantages to this approach, as well. First, the use of a single liquid containing membrane raises the possibility that the indicator fluid will pool in lower-lying areas of the membrane, negating the efficacy of upper areas. It also means that any devices formed from this fabric would have to consist of one seamless piece, as seams would be both be devoid of protection and vulnerable to leaks. Even assuming a uniform distribution of fluid, many small punctures, as those caused by a hypodermic needle, would be unlikely to be detectable. Finally, the dual membrane would be extremely inflexible.
U.S. Pat. No. 5,104,704 issued to Labes et al. (1992) uses a slightly different system, reacting dye precursor gels to produce the desired color change. This method is bulky, heavy, and expensive, and is limited to small-scale uses, such as pill bottle caps.
U.S. Pat. No. 4,424,911 issued to Resnick (1984) uses microspheres containing a substance which, when released by mechanical trauma, causes a permanent color change in the substrate paper. It is exactly this permanent change that is problematical with this method. Along with many of the aforementioned devices, its indication is irreversible. In addition, the substrate paper, especially if it is litmus as described in one embodiment, is vulnerable to "false positives" due to environmental factors.
U.S. Pat. No. 3,935,960 issued to Cornell (1976) describes a tape cover for older soda cans which comprises two dye precursors, which, upon mechanical trauma, are mixed. This device is relatively inflexible. The color change occurs at very low angles of flexion. As with many of the above devices, the tape cover indicates that a trauma or violation has occurred only in the area immediately adjoining the site of the trauma.
U.S. Pat. No. 5,304,684 to Nishida et al. describes a process for producing methyl ethyl ketone by decomposing sec-butylbenzene in the presence of an acid catalyst.
Accordingly, besides the objects and advantages of the devices listed above, several objects and advantages of the present invention are:
To provide a membrane or garment that is light, flexible, and easily manufactured, even in complex shapes; PA1 To provide a membrane that offers equal protection in all temperature and pressure environments, even at seams, joins, and folds; PA1 To provide a membrane that is activated by any breach or puncture, no matter what the size; PA1 To provide a membrane that is reparable after puncture, and that retains its indicating qualities; and PA1 To provide a membrane that creates an indication large in size and readily apparent, even for small punctures.
Further objects and advantages will become apparent from a consideration of the following description and drawings.